Emissions regulations for internal combustion engines have become more stringent over recent years. Environmental concerns have motivated the implementation of stricter emission requirements for internal combustion engines throughout much of the world. The emissions standards are not merely regulating the pollutants emitted by an internal combustion engine that is operating at steady state. Emissions tests often include thousands of data points collected over a certain length of time and under various engine operating conditions. For example, the results of an emissions test often include emissions data from cold start-up and high engine demand situations. Consequently, engines must be designed to operate efficiently and within emissions regulations over a variety of operating conditions.
Some engines may be particularly efficient when operating under steady state conditions and after the aftertreatment components have had sufficient time to reach optimal operating temperatures. However, such systems may suffer from poor start-up performance or may emit an excessive amount of pollutants when accelerating. Specifically, compression-ignited engines (e.g., diesel engines) often emit large amounts of nitrogen oxides while accelerating or during transition periods (e.g., start-up). These peaks of nitrogen oxide emissions can result in an engine either failing to pass regulated emissions standard or may require additional aftertreatment components or sacrifice performance in order to meet the emissions standards.